The present invention relates to an improved transmission box for wheeled machine, particularly of the walking type, as well as a wheeled machine, particularly of the walking type, provided with such a transmission box.
It relates more particularly to wheeled machines whose transmission box is of the type comprising, disposed at least partially within said box, an input motor shaft driving a drive wheel to actuate at least one drive shaft of at least one machine wheel, a clutch mechanism being disposed between said drive wheel and the drive shaft of the machine wheels, this clutch mechanism being actuated by driving in rotation the drive wheel and axial movement of a member on said wheel drive shaft and be actuated by driving in rotation the drive shaft of the wheels when the motor input shaft is stopped or when the speed of rotation of the drive shaft of the wheels is greater than the speed of rotation of the drive wheel.
Most transmission boxes used in such wheeled machines comprise a clutch mechanism whose passage from the disengaged to the engaged position is controlled by means of an actuator, such as a fork, which controls the movement of the clutching members within the box. An example of such a transmission box including a clutching mechanism with an external actuator for said box is particularly described in the patent EP 0 782 820.
For simplification of construction and reduction of the control members, there have been developed so-called automatic clutches. An example of such a clutch is particularly described in the patent EP 1 198 981. In this case, it is the movement of a spring in the form of a split ring disposed coaxially to the drive shaft of the wheels, which plays the role of clutching member between a toothed wheel and a member secured in rotation to the drive shaft of the machine wheels. This solution is relatively complex to practice and does not give satisfaction in terms of reliability of the clutching and unclutching operations. Moreover, there has been noted rapid wear of the spring leading to malfunction of clutching.
As has been mentioned above, so that automatic clutching will operate, it should be true that the axially movable member be driven in movement in a first direction by a drive member, such as a powered toothed wheel, and in a second direction by the wheel drive shaft. Such is not the case with devices disclosed in U.S. Pat. No. 4,153,964 and U.S. Published Application 2003/155,204.
Thus, U.S. Pat. No. 4,153,964 discloses a member of the wheel type with a ratchet axially movable along the shaft by means of ramps 76 coacting with axles of the radial pin type 68, 66. This wheel, provided with ramps, is here maintained permanently in engagement with the shaft because in the course of its axial movement, it coacts either with the axle 69, or with the axle 68. It is thus each time the axis mounted on the guide shaft of the wheel which controls the axial movement of said wheel along this axle. Such a solution is however not transposable to an automatic clutch.
U.S. 2003/155,204 itself discloses a clutching device of the plate type constituted by an element of the plate type with notches coupled to a driven element and shown at 4 in the drawings, an element of the plate type with notches or crenalations shown at 6 in the figures and coupled to a driving element and, between said elements 4 and 6, an intermediate clutch plate shown at 50 in the figures.
This clutch plate 50 comprises, on one of its surfaces, crenalations adapted to coact with crenalations on the member 6 to permit driving in rotation said clutch plate whilst on its other surface it is provided with ratchet teeth adapted to engage with the driven element 4. Under the influence of its own weight, the element 50 comes into engagement by means of its teeth with the crenalations of the member 4 so as to transmit the movement of rotation of the member 6 to the member 4. If the member 4 is moved at a speed higher than the clutch plate 50, then the arrangement of the teeth and of the crenalations permits axial movement by the member 4 of the member 50. As a result, the member 50 is not movable axially so in a controlled manner in the two directions but only in a single direction. In the other direction, it is its own weight which makes it move axially. The member 6 thus does not control the axial movement of 50. Moreover, in such an operation, the fact that positioning the support shaft of said pieces in a horizontal position is impossible. Only vertical position of such a shaft is possible.
As a result, again, this document cannot be compared to a device of the automatic clutch type because here, the clutch plate is controlled in axial movement in only a single direction.